Induction-furnace.



B. F. GEHRKENS.

INDUCTION FURNACE.

APPLICATION FILED JULY 14,1910.

1,011,769. Patented Dec.12,1911.

Witnesses: Inventor":

Edward FTGehrkens,

1 y Wgg 9 His o itornes.

I naces.

UNITED STATES PATENT OFFICE.

WARD 21". GEHRKE NS, 0F PITTSFIELD, MASSACHUSE'lTS,v ASSIGNOR TO GENERAL ELECTRIC-COMPANY, A CORPORATION OF NEW YORK.

INDUCTION-FURNACE.

Specification of Letters Patent.

Patented Dec. 12; 1911.

Application filed m 14, 1910. Serial No. 571,898..

To all 'w/mm inlay concern:

Pittsfield, county of Berkshire, State of Massachusetts, have invented certain .iew and useful Improvements in Induction-Furof which the following is a specification. I

My invention relates to electricfurnaces of the induction type and involves a furnace in which the secondary current is largely induced in the walls of'the furnace instead of entirely in the charge, the heat being communicated to the charge by conduction and radiation.

Inductionfurnaces have heretofore been built to induce a current in the charge itself. This design not only requires the charge to be conductive when the. furnace is started but it has a further disadvantage. When a very heavy current is traversin the fluid charge, a phenomenon known as t e pinch effect is apt to take place, the charge under the influence of electrical forces breaking its own circuit. The circuit may rema'in'permanently broken by non-conductive slag lodging in the break. According to my invention this difliculty is overcome by providing as part of the furnace structure a secondary having a low resistance zone and a relatively high resistance zone, the high resistance zone formingpart of the wall of the crucible or chamber containing the charge. The heat generated in thehi h resistance zone is communicated to the c arge with which it is either in immediate contact, or separated only by a refractory lining.

My invention will be more fully described in connection with the accompanying drawings in which-- Figure 1 is a perspective view of a single phase induction furnace constructed in accordance with my invention; Fig. 2 is a plan view of a somewhat modified form;- F1 3 is a diagram of connections, and Fig. A; is a plan view of a three-phase furnace.

Referring to Fig. 1, the furnace crucible or meltin chamber 1 consists of a metal shell 2, w ich invpart forms the secondary.

of the furnace, as will be presently explained. The primary coils 3, 3 are wound on the iron core 4 and for single phase operation aieconnected in series or parallel, a series connection being shown in Fig. 3. The coils are shown inv Fig. 3 as being connected to the secondary of a feeding transformer 5, to represent any source of energy. The secondary windings, as they may be called, surrounding the primary coils consist of some refractory metal such as steel, ,or an alloy consisting of sixty-two part-s nickel,

nineteen parts iron, eleven parts chromium,-

and eight parts manganese. This alloy is known as calorite. Each secondary has a massive relatively low resistance zone 6 and zone 7 of smaller cross-section and hence of relatively high resistance. The inside surface of the furnace chamber 1 may be covered with a suitable refractory insulating lining but this may in some cases be omitted, especlally when a relatively low melting point metal is to bejmelted in the furnace, such as brass or aluminium. The'spout .8, provided with a' suitable plug, serves for the removal of the melted charge.

When an alternating current is impresse on the primary windings of the furnace. a current is induced inthe usual well understood manner in the secondary windings surrounding the same. Very little heat is-generated by the passage of this current in the relatively low resistance part of the secondary 6, the heat being chiefly generated in the high resistance portion 7. No current will flow in the walls 9, 9'-connecting the two turns of secondary as these walls form part of a circuit 'entirelyinclosing all of the legs of the magnetic system when taken as a' .unit by' itself. A very low voltage is generated in the secondary .windings and, therefore, even when no lining is provided to insulate the charge from the secondary, very little current is diverted from the same by the .charge'as this current would encounter two contactresistances which are relatively considerable vatthe very 'low voltage, especially when theinterior surface of the furnace crucible-is oxidized. y

In some cases it isadvisable to construct the high resistance part of the crucible as a complete shell surrounding the primary windings and connected by side walls to form a charge-receiving chamber. A relatively massive wall, or jacket, consisting of some suitable metal of high conductivity is cast around the high resistance wall so as to be in direct metallic contact therewith at the outer portion of the furnace. This form is illustrated in the furnace shown in Fig. 2, the highfresistancepart of the furnace being indicated by the portion 10 and the low resistance massive partby the portion 11 The same construction may, of course, be used with a three-phase, or any other design of furnace, a three-phase furnace being illustrated by Fig. 4. In either of the modifications, the only part of the circuit to which voltage and current is induced is that art which completely surrounds one leg the magnetic circuit. 'The low resistance massive portion 11 will reduce the heating in the portion throughout the region in which it is in contact with the same by shunting current therefrom.

It Wlll be readily seen from the above description that in no case can the electrical circuit in which the secondary current is flowing interrupt itself by breaking its circuit accordin to the pinch effect.

What I claim as new, and desire to secure 'by Letters Patent 'of the United States,

1. In an induction furnace, the combination of a. charge-receiving chamber, a primary, anda secondary inductively related thereto and having zones of unequal resistance, a zone of relatively high resistance forming part of said charge-receiving cham- 1 2. In an induction furnace having a charge-receiving chamber, the combination of a primary, and a secondary inductively related thereto, said secondary consisting of a metallic shell having zones of unequal cross-section and corresponding unequal resistance, the zone of higher reslstance forming part of said char e-receiving chamber.

'3. In an induction urnace, the combination of a primary inductive winding, a secondary winding surrounding the same, and a charge-receiving chamber, a section of the walls of said chamber forming a portion of said secondary winding.

4. In an lnduction furnace having a charge receiving chamber, the combination of a primary winding and a secondary winding surrounding the same consisting of a conductive wall, including a section of relatively high resistnce which forms a part of the charge-receiving chamber.

-5. In an induction furnace having a charge-containing crucible, the combination of a primary winding, and a secondary winding in inductive relation therewith, said secondary having a zone of relatively highmesistance, said zone forming part at least of said crucible.

In witness whereof, I have hereunto set my hand this 12th day of July, 1910.

' EDWARD F. GEHRKENS.

Witnesses:

MAGNUB UNGER, HERBERT W. ANDREWS. 

